240 VDC Battery Bank

[Badger]

So, I might have an opportunity to pick up a 4.2kw UPS cheap and use it as an inverter for a future solar/wind project, but I found out the battery bank is 240 VDC.  It's meant to be powered from 240 AC or 208, and the output is selectable to 240 and 208 as well, so I guess that's why the battery bank voltage is so high.  Is this thing worth anything with the voltage so high?  I couldn't find a charge controller with a bank nominal voltage above 120 vdc.  Any ideas?

[birdhouse]

just a stab in the dark, it's probably made up of 6v or 12v individual batteries.  you could probably re-string them into 12v, 24v, or 48v... 

how old are they?

adam

[Badger]

Your right, it's made of 20 - 12V batteries tied together.  Not sure on the age, but probably 5-10 years old.  That would be great if I could re-string them to a lower voltage, but I'm not sure if the inverter will accept a lower bank voltage for an input, the user guide says something about an alarm going off if the battery voltage drops below 140V, and it will shut down.  I'll have to ask the manufacturer, there isn't much documentation on it.

[bob g]

i literally would not touch that thing with a 10ft pole, (a fiber glass pole)!

it is likely the batteries are at their end of life anyway, and messing with them in that string is asking to be hurt really bad should one of the batteries develop an internal short.

i had one of these units, a 3phase input and output 15kva with 240vdc front end, one of the batteries failed and it made a nice hole out through 3 layers of 1/8" steel casing. starting with a hole about the size of a half dollar, next plate about the size of a quarter and the final sheet about the size of a dime.

aside from that very real concern is one of electrocution, dc at that elevated voltage has a way of reaching out and touching you. once it gets its hold on you it is much more of a hold than 240vac delivers.

my vote is pass on it, unless the batteries have been replaced recently, and you can get them out safely, and part out the rest of the unit.

it just isn't worth the risk

at 4.2kva there are many other ups systems available that use a more realistic 48vdc front end out there.

bob g

[thirteen]

You might get things and test the batteries and be able to make a good bank, as for the inverter it you might also be able to change wiring inside for other use for your system. that much dc voltage will kill or shorten the fingers and toes. I would also double check the voltage just to be sure. best of luck .

[Badger]

Thanks for the advice!  I think I'll let it go, unless somewhere here would want it.  Yeah, that kind of voltage scares the bejeezus out of me, I would be very hesitant to even think about taking it apart.  I might check on the batteries, but it's meant to run at full load for only 10 minutes, so I think they are little 9 Ah batteries, not sure how useful they would be.  I asked the manufacturer if the inverter could run on a lower voltage, and they said no (not too surprised), it puts out 240ac.  I'll look into it a little more, but if anyone cares, its a Minuteman MCP6001.

In a few months, the place I work is replacing some much bigger inverter/banks, a 4.5kva and 10 kva that can run a full load for 90 minutes.  They are all 12 v, 80 ah batteries, 40 of them are from 1998, and 20 look to be only a few years old.  I could never use that many, but if someone was interested, I could try and recover them.  I'm in central Indiana...  If anyone knows of a nonprofit involved with renewable energy, let me know, seems like we are always scrapping useful things (test equipment, grounding, hvac, batteries, inverters, etc.)